On airframe such as aircraft, images (aerial photographs) of the ground surfaces have been acquired by operating frame sensor type digital cameras, and then, changes of buildings have been detected based upon the acquired aerial photographs. Recently, technical ideas have been considered whereby, for example, disaster-affected situations where disasters such as earthquakes happen to occur can be grasped based upon detection results of changes in building shapes by utilizing the above-mentioned aerial photographs.
Conventionally, while aerial image data are stored in a data recording unit mounted on an airplane, the stored aerial image data are transferred to a data processing apparatus installed on the ground after the landing of the aircraft as to be processed and analyzed. The data processing apparatus installed on the ground compares and identifies an image of the ground surface which has been newly acquired with the existing image of the ground surface, to detect a change in shapes of a building.
As image comparing/identifying methods, a method of comparing aerial images with each other, a method of comparing feature points of an ortho-image with building polygon data, a method of comparing digital surface models (DSMs) with each other, and the like, have been devised.
FIG. 12 is a flow chart for describing the method of comparing the aerial images with each other. In this method, a registration (position adjustment) is performed between an aerial image which has been newly acquired and the existing aerial image which has been acquired in the past, and then detection of whether or not a building on the ground is present, and another detection of a change in shapes of the building, are performed based upon a change in luminance information between both the aerial images.
FIG. 13 is a flow chart for describing the method of comparing the feature point of the ortho-image with the building polygon data. In the above-mentioned method, firstly, an aerial image is ortho-corrected so as to produce an ortho-image. While an aerial image photographed using a frame sensor type digital camera corresponds to a central projected image, the central projected image has distortion that becomes larger toward a peripheral area of the photographed image. The ortho-correction corrects this distortion so as to produce an ortho-image which corresponds to such an ortho projected image that a ground surface is viewed from right above this ground surface. Subsequently, feature point extraction processing and the like are performed with respect to the produced ortho-image so as to extract a contour of a building (or a portion of this building), which presently appears on the ortho-image. The extracted contour is compared with such a contour of the building which is obtained from existing building polygon data and is viewed from directly above this building, and hence a change of the building is detected.
FIG. 14 is a flow chart for describing the method of comparing DSMs with each other. In this method, a DSM is produced from an aerial image, and then a difference between the produced DSM and an existing DSM is calculated so as to detect a change of a building. While a DSM corresponds to height information about a ground surface, in such a case where this DSM is produced from an aerial image, for instance, a plurality of aerial images from different flying positions are identified with each other, and then a height of a ground object is obtained based upon apparent differences between the plurality of aerial images for the same ground object.